Typically, an image-forming active region of a display unit is smaller than the physical size of the display unit. For example, a liquid crystal display comprises typically an inactive edge region of a few millimeters. The inactive edge region exists e.g. due to reasons related to mechanical construction, strength and sealing.
It may be desired that a foldable device would be capable of displaying an image which is larger than the device in its folded state. The maximum size of the displayed image is typically limited by the size of the undivided active region of a display unit, which in turn is limited by the size of the device in its folded state.
Images formed by two or more display units may be combined to form a larger image. However, the combined image is typically divided due to the inactive edge regions of the display units. Thus, the visual appearance of the image may not be satisfactory.
U.S. Pat. No. 6,486,890 discloses an apparatus for displaying images, said apparatus comprising two adjacent display screens and two magnifying lenses arranged in front of said displays in the viewing direction. The lenses are positioned at a distance upwards of the display screens such that magnified virtual images formed by the lenses are displayed without a gap between them, said virtual images constituting a larger undivided image.
Patent publication WO2004/036297A1 discloses a cover arrangement overlaying a display screen and comprising a generally planar portion and an edge portion, the latter comprising further a light-bending region. The light-bending region provides graded magnification that optimizes the viewing across a junction between display screens that have been arranged adjacent to each other.
The aforementioned prior art solutions for providing a combined image rely on altering significantly the magnification of the view in the neighborhood of the edges of the separate adjacent displays. This causes a need to manufacture optical overlay components that have graded local magnification properties, i.e. the provided magnification is different in different parts of said components. This not only complicates the manufacturing of such components, but also creates a need to have them accurately positioned with respect to the display screens.